2. What about the Higgs Boson?

3. What precisely is the Higgs? We describe dynamics of a system via a Lagrangian – One can completely replicate all of Newtonian physics – Physical theories will in general have an associated Lagrangian (from which one can predict “laws of motion”) – One problem: mass terms, which are needed to represent the particle‘s masses, destroy the fundamental symmetries of the theory. (BAD!) The Higgs mechanism is a way to subvert this. – Assume: all particles are massless (in some fundamental theory of the Universe) – Assume: a field, called the Higgs field, permeates all of space. The Higgs boson is an excitation of the Higgs field (just as the photon is an excitation of the EM field) – The SM particles acquire mass through their interactions with the Higgs field. – Particles that interact strongly with the Higgs field are interpreted as having large mass. – Those that interact weakly, we interpret as small mass. A huge success of the “Higgs mechanism” is the unification of the weak and electromagnetic forces (Electroweak theory) – Tested quite precisely, and so far passes all tests! – One iddy-biddy problem:

4. Higgs interaction, in pictures  Consider that space is filled with the “Higgs field” (no, you can’t see it)  Assume the top quark interacts very strongly with the Higgs field, and the electron interacts very weakly. t e  If you try to accelerate the top quark (through the Higgs field), it will take much longer to make it through, since it’s interacting strongly with the Higgs field along the way. On the other hand, the electron interacts very weakly, and so it makes it through very quickly!  If top takes longer to pass through, we interpret this to mean that the top quark is heavier.  This is all consistent with your notion of inertial mass, no?  Particles that do not couple to the Higgs field would then move at the the speed of light  Photons do not directly couple of the Higgs field!

5. The Hunt for the Higgs The SM does not predict what the Higgs mass is. But, the W ± mass depends on the top and Higgs mass through quantum loop corrections. Within the Electroweak theory: Precise measurements of top and W mass place constraints on the Higgs mass. Unfortunately, m W only logarithmically dependent on Higgs mass

6. Little place left to hide ! Only this little region has yet to be excluded by direct searches for the Higgs

7. How is the Higgs produced?

8. How does the Higgs decay  If there is a Higgs at ~125 GeV, then the it decays to bb ~80% of the time.  It couples to mass, so it prefers to decay to the particles with the highest mass kinematically possible.  H 0   ~ 0.2% of the time at that mass????  Didn’t I say that it doesn’t couple to photons, since photons have zero mass ?

9. LHC Data - 2011 ATLAS Experiment CMS Experiment This is mostly what all the “excitement” is about. Both experiments see a small excess at ~125 GeV/c 2 Both experiments look at many Higgs production and decay channels, but the one which appears to be most sensitive, oddly enough, is H 0   !

10. Higgs – Future Prospect If the “hint of a hint” at 125 GeV is really the Higgs, CMS and ATLAS should have a clear signal by the end of 2012. They will collect ~3-5X more data in 2012, so this small excess should become quite significant. If it was just a cruel trick of nature, then we go back to the drawing board…. Cuz something is really wrong! So, keep your eyes & ears open !